This invention relates generally to off-road motor vehicles, such as tractors, and more particularly, to a closed center hydraulic system providing hydraulic power for operating the tractor steering mechanism, the three-point lift mechanism and the remote directional valves for operatively powering implements coupled to the tractor.
Agricultural tractors are typically provided with a plurality of directional remote valves for the connection of hydraulic lines thereto for the operative powering from the tractor's hydraulic system the hydraulic components of an implement attached to the tractor. The tractor hydraulic system is also utilized to provide hydraulic power for the operation of certain on-board hydraulic components, such as the tractor's steering mechanism and the three-point lift linkage. The various hydraulically powered components require different demands on the hydraulic system, which must be configured to adapt to the different hydraulic demands.
Within the tractor on-board hydraulic system, and also within the hydraulic components driven from the tractor on-board hydraulic system, are mechanical devices, such as gears, that can become damaged during their operation. When such devices are damaged, metal chips typically enter the flow of hydraulic fluid and can contaminate other mechanical devices, causing further damage and additional contamination of the hydraulic system. Filters and screens are normally provided within the flow path of hydraulic fluid within the system to remove such contaminates. The servicing of hydraulic system filters and screens is often cumbersome due to the location of the screens, which is particularly true with agricultural tractors.
The reservoir or sump for the hydraulic system on agricultural tractors is usually located within the center gear hosing for the rear drive axle, so as to provide lubrication for the drive gears transferring rotational power from the drive shaft operably driven from the engine to the rear drive wheels of the tractor, as well as provide a large reservoir for the hydraulic system. It would be desirable to provide a screen mechanism for the removal of large contaminates from the hydraulic system of an agricultural tractor that facilitates the installation and removal of the screen member.
When the tractor is operated in cold weather conditions, the start-up of the tractor engine and the resultant need to have hydraulic pressure within the tractor on-board hydraulic system can result in damage to the system components. The low ambient temperatures cause the hydraulic fluid to thicken, which increases the resistance the fluid has to passing through filters. As a result, some of the filters can be bypassed over a pressure relief line, allowing contaminants to bypass the filter and flow through the hydraulic system where damage could occur. Accordingly, it would be desirable to provide a reservoir heater operatively associated with the intake of hydraulic fluid from the reservoir.